The decorative laminates known to date all consist of a surface layer impregnated with melamine resin and a plurality of lower layers impregnated with phenol resin, also referred to as core layers. So-called kraft paper is used for the lower layers. The surface is a special decorative paper which, by printing with special colors, represents the decorative surface.
These decorative laminates have the disadvantage that they have a strong intrinsic odor of phenol and even traces of unconverted phenol are still detectable in the laminate, depending on the production conditions. Phenol is toxicologically unsafe. Particularly in the recycling process and during incineration, even more toxic substances may form through thermal secondary reactions with other substances present, especially with halogen-containing organic compounds.
The phenol resin is produced exclusively in strongly basic reaction media with the use of alkali metal hydroxides. In order to ensure better reactivity of the resins during the impregnation process and especially during the curing process on pressing, it is necessary to adjust the pH of the kraft paper to about 8.5 to 9.0.
It is known that a reduction in the phenol content can be achieved by adding urea to the resin batch. However, a disadvantage thereby is that, with the use of urea contents above 10% by mass of urea in the solid resin, the good water resistance of the phenol resin decreases very greatly. The reason for this is that the urea does not react under the reaction conditions for phenol resins (pH>8) and readily leads to increased water absorption of the resin.
A further disadvantage of the production of decorative laminates from the combination of melamine resin-impregnated and phenol resin-impregnated papers consists in an incompatibility at the interfaces. This is due to the different catalysts which shift the pH of the impregnated papers into the acid or into the basic range. In the case of extreme differences, for example a pH of 9 in the case of the phenol resin-impregnated papers, delamination processes may readily occur at the interfaces.